The present invention relates generally to microfluidic systems, devices, and methods. More particularly, the present invention provides structures and methods that are useful for handling and sequentially introducing large numbers of samples into devices having microfluidic channels.
Considerable work is now underway to develop microfluidic systems, particularly for performing chemical, clinical, and environmental analysis of chemical and biological specimens. The term microfluidic refers to a system or device having a network of chambers connected by channels, in which the channels have microscale dimensions, e.g., having at least one cross sectional dimension in the range from about 0.1 xcexcm to about 500 xcexcm. Microfluidic substrates are often fabricated using photolithography, wet chemical etching, injection molding, embossing, and other techniques similar to those employed in the semiconductor industry. The resulting devices can be used to perform a variety of sophisticated chemical and biological analytical techniques.
Microfluidic analytical systems have a number of advantages over conventional chemical or physical laboratory techniques. For example, microfluidic systems are particularly well adapted for analyzing small samples sizes, typically making use of samples on the order of nanoliters and even picoliters. The channel defining substrates may be produced at relatively low cost, and the channels can be arranged to perform numerous specific analytical operations, including mixing, dispensing, valving, reactions, detections, electrophoresis, and the like. The analytical capabilities of microfluidic systems are generally enhanced by increasing the number and complexity of network channels, reaction chambers, and the like.
Substantial advances have recently been made in the general areas of flow control and physical interactions between the samples and the supporting analytical structures. Flow control management may make use of a variety of mechanisms, including the patterned application of voltage, current, or electrical power to the substrate (for example, to induce and/or control electrokinetic flow or electrophoretic separations). Alternatively, fluid flows may be induced mechanically through the application of differential pressure, acoustic energy, or the like. Selective heating, cooling, exposure to light or other radiation, or other inputs may be provided at selected locations distributed about the substrate to promote the desired chemical and/or biological interactions. Similarly, measurements of light or other emissions, electrical/electrochemical signals, and pH may be taken from the substrate to provide analytical results. As work has progressed in each of these areas, the channel size has gradually decreased while the channel network has increased in complexity, significantly enhancing the overall capabilities of microfluidic systems.
One particularly advantageous application for microfluidic techniques is to screen collections of large numbers of samples. There has long been a need to rapidly assay numerous compounds for their effects on various biological processes. For example, enzymologists have long sought improved substrates, inhibitors, and/or catalysts for enzymatic reactions. The pharmaceutical industry has focussed on identifying compounds that may block, reduce, or enhance the interactions between biological molecules, such as the interaction between a receptor and its ligand. The ability to rapidly process numerous samples for detection of biological molecules relevant to diagnostic or forensic analysis could also have substantial benefits for diagnostic medicine, archaeology, anthropology, and modern criminal investigations. Modern drug discovery has long suffered under the limited throughput of known assay systems for screening collections of chemically synthesized molecules and/or natural products. Unfortunately, the dramatic increase in the number of test compounds provided by modern combinatorial chemistry and human genome research has overwhelmed the ability of existing techniques for assaying sample compounds.
The throughput capabilities of existing sample handling and assaying techniques have been improved using parallel screening methods in a variety of robotic sample handling and detection system approaches. While these improvements have increased the number of compounds which can be tested by a system, these existing systems generally require a significant amount of space to accommodate the samples and robotic equipment, and the sample handling equipment often has extremely high costs. Additionally, large quantities of reagents and compounds are used in performing the assays, which reagents have their own associated costs, as well as producing significant waste disposal problems. Use of small amounts of test compounds with these existing techniques can increase the errors associated with fluid handling and management due to evaporation, dispensing errors, and surface tension effects.
A high throughput screening assay system using microfluidic devices has previously been described. Published P.C.T. Patent Application No. WO 98/00231, the full disclosure of which is hereby incorporated by reference for all purposes, describes a microlaboratory system which can sequentially introduce a large number of test compounds (typically contained in multi-well plates) into a number of assay chips or microfluidic devices. This advantageous system allows testing of a large number of sample compounds with a compact sample handling arrangement, while the manipulation of picoliter or nanoliter volumes of chemicals can both enhance the speed of each chemical analysis and minimize sample and waste product volumes. Hence, such a microlaboratory system represents a significant advancement for handling and testing large numbers of chemical and biological compounds.
Although the proposed application of microfluidic devices to high throughput screening provides a tremendous increase in the number of sample compounds which can be cost effectively tested, still further improvements would be desirable. In particular, it would be helpful to develop devices and methods which were adapted to efficiently handle the tremendous number of sample compounds that might be tested with such a system. It would be best if these sample handling techniques were flexibly adaptable to the wide variety of analyses that might be performed in a microfluidic screening system. Such sample handling systems should be tailored to take advantage of the strengths of a microfluidic analytical device, while minimizing any limitations of microfluidic analysis, and while accommodating any particular sensitivity of these new structures which might otherwise induce error. Ideally, all of these enhanced capabilities will be provided in a compact, high throughput system which can be produced at a moderate cost.
The present invention generally provides improved systems, devices, and methods for analyzing a large number of sample compounds. In many embodiments, the samples will be contained in standard multi-well microtiter plates, such as those having 96, 384, 1536, or higher numbers of wells. These multi-well plates will typically travel along a conveyor system between an input stack and an output stack. One or more test stations, each having a microfluidic device, will be disposed along the conveyor system. At the test station, each multi-well plate can be removed from the conveyor, and the wells of the multi-well plate will typically be sequentially aligned with an input port of the microfluidic device. After at least a portion of each sample has been injected into the microfluidic channel system, the plate will be returned to the conveyor system. Pre and/or post processing stations may be disposed along the conveyor system, and the use of an X-Y-Z robotic arm and a novel plate support bracket allows each of the samples in the wells to be accurately introduced into the microfluidic network. This arrangement avoids having to move the microfluidic device or its port between entering of the samples, significantly simplifying the chip interface structure. In the exemplary embodiment, a clamshell structure having a hinged lid releasably supports the chip while providing and/or accommodating the electrical, fluid, optical, structural, and any other interface connections between the microfluidic device and the surrounding high throughput system.
In a first aspect, the present invention provides a system for analyzing a large number of sample compounds. The system comprises a plurality of arrays, each array having a plurality of regions for holding samples. An array transport system translates the arrays sequentially along an array path. At least one microfluidic device will be disposed off of the array path. The microfluidic device has a sample input port and a channel system with a channel cross sectional dimension in the range from about 0.1 xcexcm to about 500 xcexcm. A transportation mechanism moves each array from the array path and sequentially aligns the regions of the array with the port of the microfluidic device.
Preferably, a microfluidic device interface structure supports the microfluidic device (and its port) at a fixed position. This interface structure will preferably comprise a clamshell having a lid pivotally coupled to a base so as to restrain the microfluidic device therebetween. A window through the lid or base facilitates optically coupling an optical detection system to the channel system of the microfluidic device for monitoring an optical characteristic of a reaction within a channel system. Electrodes extending from the base or lid can couple an electrical potential source to fluid within the channel system through electrode ports of the microfluidic device for electrokinetically transporting the fluids within the microfluidic channel system.
In the exemplary embodiment, the array comprises multi-well plates, and the transportation system for moving the plates from the conveyor system includes a robot arm having at least two, and preferably three degrees of freedom. Where the plates define a planar array of wells, such a robotic arm allows the port to be selectively aligned with any of the wells (along the X and Y axes), and allows the plate to be lifted to bring the sample within each well into contact with the input port (along the Z axis). By using a plate support bracket which is narrower than the plate, lifting pins adjacent to the conveyor system can engage exposed peripheral portions of the plate""s lower edge to transfer the plate between the bracket and the conveyor system. This avoids complex robotic grasping mechanisms supported by the robotic arm. Pre and/or post testing stations may be disposed along the conveyor system. Such stations might include a sample management station, for example, a card reader which enters data from a bar code affixed to each plate so as to identify the samples thereon. Alternatively, reaction stations may be positioned before and/or after the test station, for example, to controllably dilute the samples contained in the wells of a plate prior to testing, for reconstituting test compounds in an aqueous buffer, and the like. The use of a bi-directional conveyor belt and/or programmable transportation mechanisms provides flexibility in defining different testing sequences. For example, a single sample disposed within one well of a plate might be moved back and forth between a dilution station and the test station to provide data at different reaction times, multiple concentrations, and the like.
In another aspect, the present invention provides a system for analyzing a large number of samples. The system comprises a plurality of plates, each plate having an array of wells. A plate conveyor translates the plates along a plate path. At least one test station will be disposed along the plate path. The at least one test station includes a microfluidic substrate having a sample input port in fluid communication with at least one channel with a cross sectional dimension in a range from about 0.1 xcexcm to about 500 xcexcm. The test station further includes a plurality of lifting pins to sequentially lift the plates from the conveyor, and a plate transportation mechanism. The transportation mechanism moves the lifted plates from the plate path with at least two degrees of freedom to sequentially align the wells of the plate with the input port of the substrate. The transportation mechanism comprises a rigid plate support bracket that fittingly receives the plate when the plate rests on the bracket.
The present invention also provides a method for testing a large number of samples. The method comprises arranging the samples in a plurality of wells. The wells are disposed in a plurality of plates, and the plates are transported along a plate path. The plates are removed from the path and the wells are sequentially aligned with a fluid inflow port of a microfluidic device. The samples are transferred sequentially from the wells into a channel system, the channel system having a cross sectional dimension in a range from about 0.1 xcexcm to 500 xcexcm.
The present invention further provides a system for analyzing a large number of sample compounds. The system comprises a plurality of arrays, each array having a plurality of regions for holding samples. An array transport system translates the arrays sequentially along an array path. A batch process station is disposed along the array path for simultaneously processing the samples of each array while the array will be disposed at the batch station. At least one sample test device will be disposed off the array path. The test device has a sample input port, and a transportation mechanism moves each array from the array path and sequentially aligns the regions of the array with the port of the test device.
In another aspect, the present invention also provides a support structure for robotic manipulation of a plurality of assay samples. The assay samples are disposed in wells of a plurality of plates, each plate having an upper surface and a lower surface with front, back, left, and right edge surfaces extending therebetween. The support structure comprises a beam defining a proximal end and a distal end with an axis therebetween. An upwardly oriented tab near the distal end of the beam inhibits axial movement of the plate when the plate rests on the support structure. A pair of horizontally opposed sidewalls adjacent the proximal end of the beam fittingly receive left and right edge surfaces of the plate when the plate rests on the support structure.
The invention also provides a related method for manipulating a plurality of assay samples. The method comprises distributing the assay samples in wells of a plurality of plates. Each plate has an upper surface and a lower surface with front, back, left and right edge surfaces extending therebetween. The plates are positioned on a support structure such that a beam of the support structure extends from adjacent the front surface of the plate to adjacent the back surface of the plate. An upwardly oriented tab near the distal end of the beam inhibits movement of the plate. The assay samples within the wells of the plate are moved by translating the bracket.
In yet another aspect, the present invention provides a system for analyzing samples. The system comprises a microfluidic device having a channel system with a channel cross sectional dimension in the range from about 0.1 xcexcm to about 500 xcexcm. An interface structure supports the microfluidic device, the structure comprising a base and a lid movably coupled to the base so that the microfluidic device will be restrainable therebetween. At least one of the lid and the base define a window. An optical detection system will be optically coupled to the channel system through the window of the interface structure for monitoring an optical characteristic of a reaction within the channel system.
In yet another aspect, the present invention provides a system for analyzing samples. The system comprises at least one microfluidic device having a channel system with a channel cross sectional dimension in the range from about 0.1 xcexcm to about 500 xcexcm. A support structure supports the microfluidic device, the support structure including a base and a lid. The lid rotatably engages the base so as to move between an open position and a closed position. At least one electrode will be mounted within the lid. The at least one electrode will extend into the channel system of the microfluidic device when the lid is disposed in the closed position. The at least one electrode will be clear of the microfluidic device (so that the microfluidic device is removable from the support structure) when the lid is in the open position.
In yet another aspect, the present invention provides a system for testing a large number of sample compounds. The system comprises at least one sample array. A sample transfer mechanism distributes the samples from the sample array to a plurality of reusable arrays. An array transport system translates the reusable arrays sequentially along an array path from the sample transfer mechanism. At least one microfluidic device will be disposed along the array path. The device has a sample input port that admits the samples from the reusable arrays into a channel system with a channel cross sectional dimension in a range from about 0.1 xcexcm to about 500 xcexcm. A cleaning system will be disposed along the array path for removing the samples from the arrays.
Preferably, the array path defines a closed loop, so that the reusable arrays are loaded with samples, the samples are moved to and tested in the microfluidic device, the tested arrays are cleaned of the tested samples, and the arrays are loaded with new samples continuously. This may allow the use of specialized arrays incorporating electrodes to facilitate electrokinetically introducing the samples into the microfluidic devices. Advantageously, such a reusable array system avoids the waste problems associated with large numbers of disposable multi-well plates when testing libraries of test compounds. Such libraries will typically include at least 1,000 different test compounds, the libraries preferably having at least 10,000 test compounds, and often having over 100,000 different test compounds.
In another aspect, the present invention provides a screening system for screening a large number of test compounds in a screening assay. The system comprises a first sample array or set of sample arrays comprising at least 1,000 different test compounds. Each of the test compounds is disposed in a separate region of the first sample array or set of sample arrays. A dilution system separately samples each of the different test compounds and delivers each of the different test compounds to a different region on a second sample array or set of sample arrays. The second sample array or set of sample arrays comprises a plurality of different regions for retaining a sample. A screening apparatus is provided for contacting each different test compound with a biochemical system, and for monitoring an effect, if any, of the test compound on the biochemical system. A sampling system samples each of the test compounds from the second sample array or set of sample arrays, and delivers each of the test compounds to the screening apparatus. A sample array recycling system removes the different test compounds from the second sample array or set of sample arrays, dries the second sample array or set of sample arrays, and moves the second sample array or set of sample arrays into position to receive test compounds from the dilution system.